Dasatinib Versus Imatinib in Patients (Pts) with Chronic Myeloid Leukemia in Chronic Phase (CML-CP) Who Have Not Achieved an Optimal Response to 3 Months of Imatinib Therapy: Dascern

Introduction: Treatment with dasatinib, a second-generation tyrosine kinase inhibitor (TKI), has resulted in high rates of cytogenetic and molecular responses for pts with CML-CP, both as initial therapy and after failure of other therapies. A reduction in BCR-ABL1 transcript levels to ≤ 10% on the International Scale (IS) at 3 mo is associated with an improved probability of deep molecular responses and superior progression-free and overall survival (PFS and OS). In DASISION, considerably more pts treated with dasatinib achieved BCR-ABL1 ≤ 10% IS compared to imatinib. BCR-ABL1 ≤ 10% IS at 3 mo is considered an optimal response by international guidelines; however, approximately one-third of pts with CML-CP on first-line (1L) imatinib will not achieve this threshold. Clinical studies exploring the potential benefit of early switching to dasatinib in pts with less than optimal responses on initial imatinib treatment have not been reported.

Methods: DASCERN (NCT01593254) is a randomized, open-label, international phase 2b trial in adult pts with CML-CP who had achieved complete hematologic response (CHR) but who had BCR-ABL1 > 10% IS at 3 mo after initial treatment with 400 mg imatinib once daily (QD). Imatinib must have been started within 6 mo of the initial CML-CP diagnosis. Pts were randomized 2:1 to receive 100 mg dasatinib QD or continue imatinib at ≥ 400 mg daily with the option for dose escalation. Pts initially randomized in the imatinib cohort who met European LeukemiaNet 2013 failure criteria after randomization and without dasatinib-resistant mutations were crossed over to the dasatinib arm. The primary endpoint in DASCERN is the rate of MMR (BCR-ABL1 < 0.1% IS) at 12 mo after day 1 initiation of 1L imatinib (9 mo after randomization). Secondary endpoints include time to MMR, OS, and PFS (progression was defined as transformation to accelerated/blast phase or death). Tertiary endpoints include safety and tolerability profile of both treatment arms and cytogenetic response over time.

Results: All 260 randomized pts (dasatinib: n = 174; imatinib: n = 86) had a minimum follow-up of ≥ 12 mo from the last pts 1st visit (Sokal scores: 28% low, 30% intermediate, 24% high, 18% unknown; median age 37 y [range 18-82, 95% were < 65 y]; 78% male; 73% Asian). All pts had e13a2 or e14a2 transcript types. At the time of analysis, 84% of pts were continuing in the study. Median daily dose was 100 mg QD (range 26-142) for dasatinib and 400 mg QD (range 129-825) for imatinib. Median treatment duration was 111 wk (774 d) in the dasatinib arm and 68 wk (477 d) in the imatinib arm; 42 (49%) imatinib-randomized pts crossed over to dasatinib. Rate of MMR at 12 mo in the intent-to-treat population was 29% (95% confidence interval [CI] 22, 36) for dasatinib and 13% (95% CI 7, 22) for imatinib (P = 0.005); median time to MMR was 14 mo (range 12-18) for dasatinib vs 20 mo (range 14-26) for imatinib (P = 0.053). No differences in the rate of progression or OS were observed between treatment arms. No new safety signals were observed for either treatment arm and the early switch to dasatinib did not increase the toxicity rate. Treatment-emergent pleural effusion (PE; any grade) occurred in 11 (6%) pts randomized to dasatinib and 3 (7%) imatinib-randomized pts who crossed over to dasatinib; treatment-emergent PE grade 3/4 occurred in 1 (1%) pt randomized to dasatinib and 2 (5%) pts randomized to imatinib who crossed over to dasatinib. Hematologic toxicity was similar between treatment arms: neutropenia grade 3/4 occurred in 18 (11%) pts randomized to dasatinib and 12 (29%) pts randomized to imatinib who crossed over to dasatinib; thrombocytopenia grade 3/4 occurred in 18 (11%) pts randomized to dasatinib and in 7 (17%) pts randomized to imatinib who crossed over to dasatinib. Two dasatinib-treated pts discontinued due to hematologic toxicity (1 neutropenia, 1 thrombocytopenia).

Conclusions: Early results from DASCERN show that pts with suboptimal responses to imatinib at 3 mo who switched to dasatinib had a significantly increased rate of MMR at 12 mo compared to pts who remained on imatinib. Longer follow-up is required to assess the impact of early switching on PFS and OS, and achievement of deep molecular responses.